The present invention is concerned with photography and, more particularly, with diffusion transfer processes.
The present invention is especially related to silver and color diffusion transfer process of the type wherein a transfer image is obtained in a single step by treating an exposed photosensitive element with a layer of a suitable processing solution to provide, as a function of development, an imagewise distribution of image-forming components, and transferring at least a portion of the image-wise distribution of image-forming components to a superposed image-receiving layer to form a transfer image thereon.
In silver diffusion processes, an exposed photosensitive silver halide emulsion is developed and almost concurrently therewith a soluble silver complex is obtained by reaction of a silver halide solvent with the unexposed and undeveloped silver halide of said emulsion. Preferably, the photosensitive silver halide emulsion is wet with a layer of processing composition which is spread between the photosensitive element comprising the silver halide emulsion and an image-receiving element. The processing composition effects development of the latent image in the emulsion and substantially contemporaneous therewith forms a soluble silver complex, for example, a thiosulfate, with undeveloped slver halide. This soluble silver complex is, at least in part, transferred to the image-receiving element and the silver thereof is largely precipitated thereon to form the transfer image.
In color diffusion transfer processes, a photosensitive element including a silver halide emulsion layer is exposed to create therein a latent image. The latent image is developed and, concurrent with and under the control of this development, an imagewise distribution of mobile color-providing substances is formed. At least a portion of these color-providing substances of image dyes or image dye intermediates is transferred to a superposed image-receiving layer to form a colored image thereon. As examples of such processes, mention may be made of the processes disclosed and claimed in U.S. Pat. No. 2,983,606, wherein dye developers (i.e., compounds which contain in the same molecule both the chromophoric system of a dye and also a silver halide developing function) are the color-providing substances, the processes disclosed and claimed in U.S. Pat. No. 2,647,049, issued July 28, 1953, to Edwin H. Land, wherein color developers are employed to develop the latent image and color couplers are the color-providing substances, and the processes disclosed in U.S. Pat. No. 3,087,817 issued Apr. 30, 1963, to Howard G. Rogers, wherein complete, preformed dyes are used as the color-providing substances and the processes disclosed in U.S. Pat. No. 3,443,940, issued May 19, 1969 to Stanley M. Bloom and Howard G. Rogers, wherein a compound which is immobile and non-diffusible in the processing fluid, but which, upon development of the emulsion, undergoes a ring-closing reaction to split off a mobile and diffusible color-providing material which is transferred to a dyeable stratum.
In the most commonly employed method for carrying out such diffusion transfer processes, a layer of the processing solution is applied between the photosensitive element and a superposed image-receiving element, and the imagewise distribution of image-forming components is transferred through the layer of processing solution to the image-receiving layer. In particularly useful embodiments, the processing solution is dispensed between th photosensitive element and the image-receiving element from a rupturable container such as disclosed in U.S. Pat. No. 2,543,181, by moving said container between a pair of pressure rollers such as provided in cameras such as disclosed in U.S. Pat. Nos. 2,435,717 and 3,165,0369. In especially useful embodiments, the processing solution comprises a polymeric viscosity-increasing reagent to facilitate the spreading of the solution between the photosensitive element and the image-receiving element. Such reagents generally serve to slow down the flow rate of the processing solution so that it can be more uniformly controlled and distributed between the superposed negative and image-receiving element.
Generally, the polymeric viscosity-increasing reagents which are used in the above embodiments are soluble in aqueous alkaline solutions and are inert with respect to the photographic reagents which may be present, e.g., developers, antifoggants, alkali, silver halide solvents, etc. In the past, water-soluble hydroxy-substituted polymers have been found useful. In especially useful embodiments, hydroxyalkyl ethers of cellulose, such as hydroxyethyl cellulose have been employed, as well as carboxymethyl cellulose, as is disclosed in U.S. Pat. No. 2,603,565, issued July 15, 1965, to Edwin H. Land, and which is incorporated herein by reference.
As is well known in the art, the aforementioned photographic reagents may be present in the processing composition or disposed in the film unit. Therefore, the photographic processing composition is adapted to provide, upon contact with the exposed photosensitive layer, as a function of development, an image distribution of image forming components, either by carrying the reagents in the processing composition or by the processing composition releasing or activating reagents in the film unit.
In certain instances, however, the viscosity-increasing reagents have inhibited transfer of the image-forming components or have lacked stability with respect to the ability to maintain other components of the processing composition in solution or suspension.